Glaucoma is a progressive disease of the optic nerve that left untreated can lead to irreversible loss of vision. Glaucoma results in apoptosis of the retinal ganglion cells (RGCs), including their axon and cell body. The loss of the RGC axonal bundle within the optic nerve head (ONH) leads to characteristic cupping and corresponding visual field (VF) loss. It is important to detect the disease early, as well as to monitor changes in glaucomatous damage. The clinical standard for detection of disease and its progression has been the automated perimetry and clinical assessment of the optic nerve cup. However, once moderate visual field loss occurs (in the range of −15 dB mean deviation (MD) loss or more), retest variability rises substantially and limits a reliable determination of visual field change. The population 95% confidence limits extend to nearly the entire operating range of the Humphrey Field Analyzer perimetric device.
Much effort has been devoted to studying the structural-functional (S-F) correlation in glaucoma with the hope that a good S-F correlation can help diagnose and monitor disease progression by providing complementary information. For example, a good S-F correlation would allow the objective structural assessment by optical coherence tomography (OCT) to predict the level of subjective functional damage in glaucoma. However, increased dynamic range and tighter S-F correlation is desired.
Increased dynamic range and tighter (less variable) S-F correlation can lead to the following clinical benefits: 1) Improved ability to stage the disease over the entire spectrum, not only by function, but also by structure; 2) Improved ability to confirm functional changes with corresponding structural changes, leading to improved ability to detect change; 3) Increased ease and patient tolerance of frequent testing for glaucoma progression to detect those who are progressing faster. If within individual variability (WIV) of OCT is reduced, improved clinical care can be achieved with frequent structural testing, which would be much easier for the average glaucoma patient, rather than frequent functional testing; and 4) Objective assessment of glaucoma damage becoming feasible for those patients who cannot perform VF tests (very young children, elderly with mental or physical limitations, etc.).